Theoretical analysis of effects of ferrite geometrical parameters on tokamak magnetic field perturbations

In this paper, a magneto-dynamic approach has been developed to investigate the probable enhancing effect of a magnetizing material like ferrite on the mitigation of the edge-localized mode instabilities. It has been assumed that the ferrite is placed on the first wall of the tokamak. The Landau-Lifschitz-Gilbert equation has been used to calculate the ferrite contribution to the equilibrium and the perturbed magnetic fields in the plasma. Simulations have shown that the ferrite can alter the magnetic field topology. Investigating the effects of the ferrite geometrical parameters such as the length, the width and the angle have shown that increasing the values of these parameters elevates the ferrite magnetization contribution in the plasma. Because of the type of the perturbation initially defined, this contribution was especially strong at the bottom of the ferrite. Since the ferrite can increase the total perturbation field in the plasma, it can help to mitigate the edge-localized modes by the resonant magnetic perturbation phenomenon. The simulation has shown that for an optimum geometry of the ferrite, the magnetic flux surfaces near the edge can be modified from an opened-line topology to a closed-line topology. Thus, the ferrite can prevent the magnetic flux from touching the wall which is necessary to have a good confinement and to reduce the edge instabilities.